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Flying Machines, Amazing at Any Angle

ON THE WING The wake of a hovering rufous hummingbird, top. Yellow vectors show air velocity, revealed by particle image velocimetry. The mist in the background is a cloud of laser-illuminated olive oil droplets.Credit
Bret Tobalskes

MISSOULA, Mont. — The flying abilities of even the most prosaic bird put airplane maneuvers to shame, and experts here at the University of Montana Flight Laboratory are cognizant of that every day.

“Birds can do some pretty spectacular things,” said Kenneth P. Dial, a biologist who, in 1988, founded the lab at a field station near the University of Montana. “They can go from 40 miles an hour to zero and land on a branch that’s moving, all in a couple of seconds. It’s inspiring.”

Dr. Dial and Bret W. Tobalske, a biologist and the director of the lab, are obsessed with trying to bridge the gap in flying abilities between humans and birds. At a laboratory filled with wind tunnels, high-speed cameras, lasers, surgical equipment and a device that generates clouds of olive oil, they and several graduate students try to divine the secrets of bird flight.

In a quiet field, Dr. Dial, 57, with a shaved head and goatee, stands out with his evangelical zeal about understanding bird flight. He has hosted a television show on adventures in bird-watching, and is so enthusiastic about flight that he and his son, Terry, also a biologist, are planning to fly around the world as pilot and co-pilot.

Dr. Dial’s 28 years of studying the functional morphology of all kinds of birds have led him and others at the lab to numerous insights into ecology, biodiversity, airplane design, aerospace and even paleontology. In a recent paper, Dr. Dial and a graduate student, Brandon E. Jackson, presented a novel idea about how some dinosaurs used their proto-wings — a possible step in the evolution of flight. They based their paper on the observation of day-old Australian brush turkey chicks.

The laboratory, at Fort Missoula, was once a stable for the United States Cavalry. What makes it unique as a lab, though, is its location in the wilderness of western Montana, with bald eagles, peregrine falcons, meadowlarks, ducks and other wild birds in the mountains and rivers right out the door.

Dr. Dial says some of his most important observations have been made watching a bird glide by while he is fly fishing, and then heading back to the lab with a new theory to test.

After observing woodpeckers in the lab’s wind tunnel both flying and “bounding” — gliding missilelike with their wings tucked, a behavior not previously identified in these birds — Dr. Tobalske was able to see the same gliding a few hundred yards out the door, which confirmed it was not a product of lab conditions.

One key to the insights here is a small, dark room with two 1,000-frames-per-second cameras, developed by the military to study ballistics, which slow high-speed action in high resolution. Wild birds in flight are misted with a fog of vaporized olive oil, which is illuminated by a green strobing laser operating in tandem with the camera. The system allows researchers to track the movement of misty air around the birds, showing where they are generating lift and drag. It led to the discovery here of a vortex on the leading edge of bird wings, which adds to a bird’s lift.

The birds, ranging from delicate diamond doves to burly ravens, have crystal sensors surgically implanted in their pectorals and elsewhere that measure muscle contractions as they fly.

“Pectorals are the motor for 80 percent of flight,” said Dr. Tobalske, which explains why they are the largest part of the anatomy. “That’s how birds generate enormous power and can resist fatigue, and why some can fly from one pole to the other” without stopping.

Birds are also put in wind tunnels and photographed at high speed so researchers can see in detail how they perform at 20 miles per hour or more. They are also fitted with tiny masks that measure metabolism.

CT scans are used on birds to tease out the hidden physics of flying. Using technology developed at Brown University, researchers scan birds’ bones and combine that with three-dimensional X-rays taken in flight. Together they create a very real animation of a bird in flight. “It gives you three-dimensional joint movement,” said Ashley Heers, a doctoral student doing the work.

Dr. Tobalske said, “These tools allow us to see things that have always been dreamed about.”

The lab has won National Science Foundation funding for 25 years, and published dozens of papers.

“This has been a classic area of research since Leonardo da Vinci,” said Richard O. Prum, a professor of ornithology and ecology and evolutionary biology at Yale. “Functional morphology is being left behind in a lot of places, but it’s important and they are doing some great stuff.”

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Work at the Montana lab, Dr. Prum said, has led people to realize how complex flight is and how many different things are happening when a bird flies. “What they have discovered is that bird flight is like Muhammad Ali boxing, with 15 different movements,” he said.

For example, birds clap their wings together at the peak of the upstroke during takeoff — that’s the clatter of a pigeon taking off in the park — and rotate their wings on the way down to get lift. “The wings suck in air, like a fan,” Dr. Tobalske said, “and create a jet of air below it traveling at 10 miles per hour.”

The most astounding fliers, in Dr. Tobalske’s opinion, are the world's 350 or so species of hummingbirds, which, largely because of their size, have mastered flight like no other bird. The calliope hummingbird weighs only as much as two paper clips, yet it migrates annually between Canada and Mexico.

In fact, a major theme in research here is how the morphology of the bird influences its behavior. The smaller the bird, for example, the more agile the flying — a swan may need the equivalent of two football fields to take off and get lift, while a hummingbird can rise like a helicopter. “It’s like a Porsche that can drive circles around a semi,” Dr. Tobalske said.

Photo

TAKEOFF Bret Tobalske, director of the University of Montana Flight Laboratory, holds a diamond dove in a wind tunnel fitted with high speed cameras.Credit
Janie Osborne for The New York Times

“The smaller the bird, the more viscous the air is,” he said, which is partly why hummingbirds can maneuver so well and for so long. They have evolved with greatly shortened wing bones, as well as large pectorals that allow them to beat their wings 80 times a second. “A hummingbird can hover like a helicopter for one and a half hours, nonstop,” Dr. Tobalske said. “No other bird can do that.” By comparison, pigeons produce one-tenth the number of strokes.

Implanted sensors show that a hummingbird’s wing flaps so fast that the brain is generating the muscle signal for the downbeat of its wing while the wing is still going up.

These new, deeper views into winged flight have affected other studies. Almost as an aside, the study of birds — which are widely believed to be descendants of some dinosaurs — has led Dr. Dial to a novel hypothesis.

The one-day-old Australian brush turkey, he says, may behave as theropods once did. Theropods were early winged and feathered dinosaurs that walked mainly on their hind legs and were incapable of flight.

Ground-nesting birds like the brush turkey are precocial — they hit the ground running when they are born, a crucial defense from predators. A day-old brush turkey can run straight up a rock wall or a tree, an ability that diminishes as the bird gets older.

A key to this early skill is flapping its small wings. This is not to try to fly, Dr. Dial said, but to serve the same role as a spoiler on a race car: to keep the bird on the ground so it can generate more force with its feet and climb steep walls. Dr. Dial calls it “wing-assisted incline running” and has high-speed videos of ground birds running up walls.

When the birds arrive atop a rock, and any threats have passed, they jump to the ground using their wings to slow the descent; that is how Dr. Dial believes flight may have begun. “This form of behavior — independence, locomotor capacity, parental care and development — could be similar to the life history of the theropod,” he said.

Dr. Prum called the idea intriguing. “He’s demonstrated the phenomena exists and it’s plausible,” he said. “But other plausible alternative claims are out there.”

As far as birds informing human flight techniques, Dr. Dial said he believes that the future of human flight will incorporate birds’ remarkable shape-shifting abilities. “Birds are constantly morphing, and morphing on different levels,” he said.

“A bird can look like a bullet, and two milliseconds later looks like a hang glider,” Dr. Dial said. “We have a lot more to learn about that. Imagine a 747 blasting off its wings and tail to become a bullet.”

Correction: January 6, 2011

An article on Tuesday about research into the mechanics of bird flight misstated the number of hummingbird species. It is about 350, not about 9,000. (There are approximately 9,000 species of birds over all.)

A version of this article appears in print on January 4, 2011, on Page D1 of the New York edition with the headline: Flying Machines, Amazing at Any Angle. Order Reprints|Today's Paper|Subscribe